Friedel Crafts catalysis is one of the major industrially important processes that is widely used in the synthesis of low and high volume chemicals. Acylations, benzylations, alkylations and sulphonylations giving a wide range of useful products like ketones, alcohols, alkyl aromatics and sulphones are included in this reaction. The petrochemical industry wherein a large number of alkyl hydrocarbons are produced by alkylation reactions is also a beneficiary of this reaction mechanism. The conventional catalysts used in this reaction mechanism include AlCl3, HF, H2SO4, BF3 and BPO4. Most batch processes use AlCl3 as the soluble acid catalyst since it is a powerful Lewis acid and also inexpensive. However, it is difficult to handle AlCl3 and other similar metal halides since they get easily hydrolysed. Very often these catalysts are required in stoichiometric amounts. A large inventory of these materials pose health, safety and storage problems. The traditional route of liquid phase alkylation using mineral acids and AlCl3 as catalyst suffer from the disadvantage of high capital costs, reactor corrosion, formation of by-products and the difficulty in catalyst regeneration. In recent times, attention is being focused on development of environmentally friendly catalysts for the production of intrinsically important chemicals and chemical intermediates.
The use of safe solid acids in the place of traditional Friedel Crafts catalysts and mineral acids have become important. Several alkylation reactions of aromatic hydrocarbons and functional aromatic hydrocarbons have been tried over zeolites, oxides, mixed oxides and supported oxides. Clays such as montmorillonite with an acidic function are also being considered as alternative catalysts for these reactions. Clays have also been modified for this purpose by pillaring with polyhydroxy metal cations such as Zr, Al, Cr, Ga, etc, acid activation, ion exchange with transition metals and by metal oxide impregnation.
Alkylation of phenols is important in chemicals industries particularly in the agrochemical and pharmaceutical industries. (Fiege et al, in Gerhartz W., et al eds. 1987—Valmann Encyclopedia of Industrial Chemistry, 5th edition, Wemheim, VCH Verlagsglsellaschaf; Lowenheim F. A. et al, 1975, Industrial Chemicals, A. Wiley InterScience, New York, Kirk, J., et al, 1981, Encyclopedia of Chemical Technology, 3rd edition, Wiley, New York). Alkylation of phenol methanol over various catalysts has been studied (Nozaka et al, Bull. Chem. Soc. Japan, 50, 1997, 614; Narayanan et al, J. Mol. Catal., 52, 1987, 129; Velu et al, React. Kinetic Catal. Lett. 62(2), 1997, 339 and Appl. Catal. A. General, 119, 1994, 241). Karuppanasamy et al report the alkylation of phenol with alcohol over thoria (J. Catal. 63, 1980, 433). Klemm et al report the alkylation of phenol with 2-propanol (J. Org. Chem., 45, 1980, 4326). Alkylation of isopropanol over zeolite catalyst is reported in Guo Changwan et al (Beinjing Huagon Yanjuyuan, 27(3), 1998, 163). Tertiary butylation of phenol was carried out over acid catalyst (Corma et al, J. Catal. 134, 1992, 58 and Appl. Catal. 105, 1993, 271). Peimo et al report the tertiary butylation of phenol over zeolite solid acid catalyst in vapour phase (Huadong Huadong Xueynan Xuebao, 14(4), 1998, 476; See also Chang et al—U.S. Pat. No. 5,288,927 and Kuizhang et al., Appl. Catal. A. General, 166, 1998, 89).
Alkylation of dihydroxy benzene with tertiary butyl alcohol using mineral acids was investigated by Komeev et al (USSR Patent 1583407, 1990).
The prior art processes above suffer from the following disadvantages:    1. Catalyst cannot be reused    2. Disposal of the acids used is not environmentally safe and/or economical    3. The selectivity is frequently observed to be low    4. Corrosion of the reactors and the reaction vessel    5. The process and the reactants are not easily handled    6. Large amounts of catalyst are required
It is therefore necessary to develop a process that overcomes the drawbacks enumerated above.